Oxidative Free Radical Reaction Research Articles

Acute chemical pulmonary edema with inhaled nitrogen dioxide intoxication

Nitrogen dioxide is released by the interaction of some metals with nitric acid. Inhalation intoxication with nitrogen dioxide leads to chemical pulmonary edema. This study presents the case of a patient who had acute inhalation exposure to an unidentified brown gaseous substance (presumably nitrogen dioxide) when he etched a metal product with nitric acid. Twenty-four hours after contact with the gas, he manifested signs of intoxication, such as chest pain, tachypnea, and decreased saturation. Laboratory tests revealed hemoconcentration, hyperfermentemia, and arterial hypoxemia. The X-ray image of the entire lung surface revealed a sharp increase and deformation of the pulmonary pattern due to the vascular component. The diagnosis was T65, i.e., toxic effect of other and unspecified substances. With treatment, the patients condition improved. On day 4 after therapeutic exposure, with decreased oxygen fraction in the inhaled gas mixture to 0.3, the saturation increased to 98%, and tachypnea disappeared. On day 6, with ongoing treatment (oxygen therapy, use of antioxidants, antihypoxants, anti-inflammatory, and antibacterial drugs), the inflammatory reaction stopped, the rheological properties of the blood improved, and the gas composition of arterial blood normalized, i.e., the oxygenation index was 436, which indicated the disappearance of arterial blood oxygenation disorders. During the radiological examination, the normal radiological picture of the lungs was determined. Thus, on day 6 after the start of therapy, signs of intoxication were completely stopped. Specific changes in the lungs during radiation research techniques, hemoconcentration, inflammation, and hypoxemia during laboratory blood tests should be considered prognostic signs of chemical pulmonary edema. As a pathogenetic therapy, treatment must be supplemented with drugs that stop the cascade of free radical oxidation reactions (acetylcysteine and sodium thiosulfate). Individuals exposed to nitrogen dioxide should be considered a high-risk group for lung damage and hospitalized for dynamic observation for at least 2 days. Taking into account the genotoxic effects of nitrogen dioxide, affected patients should be classified as at risk of developing neoplasms and undergo further dynamic monitoring.

Antioxidant Activity Test of Ethanolic Extract of Tempuyung Leaves (Sonchus Arvensis L.) Based on Linoleic - Thiocyanic Method

Free radicals chemically have free electrons, free radicals tend to take electrons from other molecules, which then give rise to abnormal compounds. Antioxidants are substances that can delay or prevent free radical oxidation reactions in lipid oxidation. Tempuyung leaves contain flavonoids which can act as antioxidants. This research aims to determine the antioxidant activity of the ethanol extract of tempuyung leaves using the linoleic-thiocyanate method and to determine the total phenolic and total flavonoid content using the Folin-Chiocalteu reagent method. The results showed that the ethanol extract of tempuyung leaf extract had antioxidant activity. Percentage of antioxidant activity of 10 % extract = 82.91 %, 5 % extract = 70.07 %, 1 % extract = 57.70 %, Vitamin E 1 % = 70.2 1%. Total phenolic content of 10% extract = 0.48 %, 5 % extract = 0.25 % and 1 % extract = 0.04 %. The total flavonoid content of the extract is 10 % = 0.14 %, 5 % extract = 0.07 %, and 1 % extract = 0.02 %. Pearson correlation test showed that phenolic and flavonoid compounds greatly influenced the antioxidant activity of the ethanol extract of tempuyung leaves.

AKTIVITAS ANTIOKSIDAN PADA EKSTRAK ETANOL 96% ANGGUR LAUT (Caulerpa racemosa) YANG BERASAL DARI PANTAI CIMANDIRI, KABUPATEN LEBAK-BANTEN

Seaweed is known to have the ability as an antioxidant, antibacterial, and immunostimulant. Antioxidants are compounds that can inhibit free radical oxidation reactions. This study aimed to determine the antioxidant activity of 96% ethanol extract of sea grapes (C.racemosa). Sea grapes extract (C.racemosa) for extract characteristics (moisture content and ash content), phytochemical analysis, heavy metal test, and antioxidant analysis using the DPPH method. The results of the characteristic test of the extract obtained water content (14.49%) and ash content (0.30%), these values ??did not exceed the standard extract values. The results of the phytochemical analysis showed that 96% ethanol extract of sea grapes (C.racemosa) contained steroid/triterpenoid compounds, flavonoids, saponins, and alkaloids. The levels of heavy metals found were still within safe limits, namely, lead (Pb) (TTD), mercury (Hg) (<0.001 ppm), Arsenic (As) (<0.001 ppm), and Cadmium (Cd) (0.005 ppm). The test results showed that the sea grape (C.racemosa) used was safe and free from heavy metal contamination. The results of antioxidant analysis on 96% ethanol extract of sea grape (C.racemosa) obtained an IC50 value of 237.51 mg/L. The IC50 value for quercetin is 9.52 mg/L. The results of antioxidant analysis on 96% ethanol extract of sea grapes (C.racemosa) were included in the moderate antioxidant range (100-250 mg/L). Sea grapes (C.racemosa) have the potential as a natural antioxidant.
 

The production of pro-inflammatory cytokines and the state of cellular immunity in patients with pulmonary tuberculosis with and without relapse

The purpose of the study was to conduct a comparative study of the synthesis of pro-inflammatory cytokines, the state of cellular immunity, free radical oxidation reactions and antioxidant protection in patients with pulmonary tuberculosis with and without relapse. Material and methods. The study was carried out on two groups of patients: the first group basic which included 39 patients with relapsed pulmonary tuberculosis (TBR); 2nd control group 39 patients with non-relapsed pulmonary tuberculosis (TB). Pro-inflammatory cytokines (TNF-α, IL-2 IL-6), CD-3 lymphocyte content, lymphocyte blast transformation response to phytohemagglutinin and tuberculin, NBT-test, AOPP, SOD, and catalase were determined in patients of both groups and healthy people. Results. In patients with tuberculosis with relapses, compared with patients without relapses, complaints of cough and dyspnea were more often presented, a longer duration of hospitalization, late abacillation. In patients with relapses, a pronounced suppression of the functional and specific activity of lymphocytes and neutrophils was noted, which is confirmed by high levels of lipid peroxidation (Advanced Oxidation Protein Products AORP) and low levels of the antioxidant system (SOD and catalase). The high content of pro-inflammatory cytokines in patients with relapses indicates a higher activity of the inflammatory process in these patients and corresponds to a low blast formation rate for both phytohemagglutinin and tuberculin. Conclusion. Сhanges in the content of pro-inflammatory cytokines, the state of cellular immunity and the characteristics of reactions of free radical oxidation and antioxidant protection indicate a higher activity of the inflammatory process in patients with pulmonary tuberculosis with relapses compared to patients without relapses, which led to a longer duration of hospitalization, late abacillation.

Kinetic Modeling of Homogenous Catalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid (FDCA) is a valuable biomass-based monomer with broad market prospects that can replace terephthalic acid (TPA) in all kinds of polymer applications. In this work, the homogeneous catalytic oxidation of 5-hydroxymethylfurfural (HMF) to FDCA was investigated over a Co/Mn/Br catalyst with acetic acid/water as a solvent. On the basis of free radical oxidation reaction mechanisms, one simplified main reaction kinetic model for the oxidation of HMF with six parameters was proposed, which considered the formation of FDCA and the most important intermediates. The effects of catalyst, temperature, and water content on the liquid-phase oxidation kinetics of HMF were investigated. The model fitted the experimental data well, in which only the chain initiation rate constant was found to be dependent on experimental conditions, while other rate constants can be kept constant in the investigated range. Hopefully, the kinetic model in this work can provide valuable insights for the design and optimization of the industrial process of HMF oxidation to FDCA.

Investigation of Biological and Prooxidant Activity of Zinc Oxide Nanoclusters and Nanoparticles.

Zinc oxide (ZnO) nanomaterials offer some promising antibacterial effects. In this study, a new form of ZnO is synthesized, named ZnO nanocluster bars (NCs). Herein, ZnO NCs, ZnO nanoparticles (NPs), ZnO coated with silica (ZnO-SiOA, ZnO-SiOB), and SiO2 NPs were prepared, characterized, and their antimicrobial and prooxidant activity were tested. The prooxidant activity of all nanomaterials was studied according to free-radical oxidation reactions (pH 7.4 and pH 8.5) in chemiluminescent model systems. Each form of new synthesized ZnO nanomaterials exhibited a unique behavior that varied from mild to strong prooxidant properties in the Fenton`s system. ZnO NPs and ZnO NCs showed strong antibacterial effects, ZnO-SiOA NPs did not show any antibacterial activity representing biocompatibility. All tested NMs also underwent oxidation by H2O2. ZnO NCs and ZnO NPs exhibited strong oxidation at pH 8.5 in the O2-. generating system. While, SiO2, ZnO-SiOA andZnO-SiOB possessed pronounced 60-80% antioxidant effects, SiO2 NPs acted as a definitive prooxidant which was not observed in other tests. ZnO NCs are strong oxidized, assuming that ZnO NCs provide a slower release of ZnO, which leads to having a stronger effect on bacterial strains. Thus, ZnO NCs are an important antibacterial agent that could be an emergent replacement of traditional antibiotics.

THE ROLE OF THE GLUTATHIONE SYSTEM IN MAINTAINING REDOX-HOMEOSTASIS AND ANTIOXIDANT PROTECTION IN INFLAMMATORY AND DEGENERATIVE DISEASES OF THE ORGAN OF VISION

Objective. To review and analyze literature data as well as evaluate the role of the glutathione antioxidant system in inflammatory and degenerative diseases of the organ of vision. Material and Methods. Multiple sources of foreign and domestic literature concerning the problem of oxidative stress, antioxidant protection system, glutathione and their role in inflammatory and degenerative diseases of the organ of vision were analyzed using main scientific and medical databases. More than 120 sources in the medical literature over the past 15 years were evaluated, 50 of them have been selected for final summary. Results. It was found that oxidative stress, based on free radical oxidation reactions, including LPO processes, plays a leading role in the development of inflammatory and degenerative diseases of the organ of vision. The key link in the eye’s antioxidant protection system is the glutathione system, which includes glutathione itself (GSH) and glutathionedependent enzymes: glutathione peroxidase (GPO), glutathione reductase (GR), glutathione-S-transferase (GST). Inflammatory and degenerative diseases of the eye are accompanied by reduction of the intracellular glutathione pool and imbalance between its reduced and oxidized forms (GSH / GSSG). Conclusions. Oxidative stress has a high correlation with inflammation and is the most important pathogenetic mechanism in inflammatory and degenerative diseases of the eye. The key role in antioxidant protection and maintenance of redox homeostasis of eye tissues belongs to the glutathione system, which includes GSH itself and glutathione-dependent enzymes (GPO, GR, GST). Inflammatory and degenerative processes in the eye are accompanied by decrease of the intracellular glutathione pool (GSH) and imbalance between its reduced and oxidized forms (GSH / GSSG). A shift in this balance significantly affects normal cell functioning, up to its apoptosis, and triggers multiple pathological conditions within the body, including diseases of the organ of vision.

Biochemical Aspects of Lipid Peroxidation. Modern Methods of Diagnostics of Cell Membrane Damage

The fundamentals of the biochemical processes underlying the damage of cell membranes are characterized, and modern methods of diagnosing lipid peroxidation (POL) are considered. POL is a chain reaction that provides an expanded reproduction of free radicals (reactive oxygen species), which initiate the further spread of POL. Reactive oxygen species can take an electron (s) away from molecules and, thereby, start a cascade of free radical oxidation reactions, as a result of which the substance becomes unable to perform its functions, because first of all, the oxidation of cell lipids occurs, which leads to damage to the cell membrane and cell death as a whole. High activity of sex is characteristic of many diseases. Therefore, it is important to be able to diagnose the level of oxidative stress in the body. Oxidative stress is expressed in the formation of numerous products that differ in chemical structure, lifetime, toxicity and biological activity. The analysis of POL products is of interest for assessing the level of oxidative stress in the body, for studying the toxic, metabolic and regulatory effects of this process on the body, as well as for the diagnosis of certain diseases.

Prooxidant and antimicrobic effects of iron and titanium oxide nanoparticles and thalicarpine.

The aim is to evaluate the prooxidant and antimicrobial effects of Fe3O4 and TiO2 nanoparticles and thalicarpine by luminescent and standard microbiological assays. Their effect on the kinetics of free-radical oxidation reactions (at pH 7.4 and pH 8.5) is studied in the following model systems, using activated chemiluminescence: chemical, with Fenton's reagent (H2O2-FeSO4)-for the generation of hydroxyl radicals (.OH); chemical, with oxidant hydrogen peroxide (H2O2); chemical (NAD.H-PhMS), for the generation of superoxide radicals (O2.-). Fe3O4 nanoparticles exhibit highly pronounced antioxidant properties; TiO2 nanoparticles exhibit mild to moderate prooxidant properties at neutral and alkaline conditions. Those properties are tested by the chemiluminescent method for the first time. Thalicarpine and its combination with TiO2 nanoparticles exhibit pronounced antioxidant activities at pH 8.5 which are lost and transformed into well-presented prooxidant effects at pH 7.4. That is a result-supported proof on the observed typical properties of thalicarpine and TiO2, namely antibacterial, organic-preserving and anti-pathogenic activities. The antimicrobial effect is tested on Gram-positive and Gram-negative bacteria: two strains of Escherichia coli, Bacillus cereus 1095 and Staphylococcus aureus. All bacteria are destroyed after the application of TiO2, but not Fe3O4 nanoparticles, showing their antibacterial effect. Thalicarpine, in combination with TiO2, showed even synergetic antibacterial effect.

Free radical oxidation reaction for selectively solvatochromic sensors with dynamic sensing ability

A novel BODIPY (boradiazaindacene) dye denoted as BODIPY-DT containing terpyridine unit has been designed and characterized. The dye is found to be selective and visual solvatochromic sensor toward DMF among test organic solvents. The sensing process displays time-controllable, dynamic signal outputs in the emission colors including red, purple, yellow and even white emission colors. It is presented that selective free radical oxidation reaction happens during the recognition process.

Effect of Metal Contaminants and Antioxidants on the Oxidation Stability of Argemone mexicana Biodiesel: Experimental and Statistical Study

Biodiesel’s auto-oxidation by metal catalyzed decomposition of hydroxides (ROOH) is a major hurdle restricting the commercial viability of biodiesel. This paper investigates the oxidation stability of argemone biodiesel contaminated with transition metals such as: Fe, Ni, Mn, Cu, and Co. Pure argemone oil biodiesel (ABD) has a rancimat induction period of 2.5 h which does not satisfy the ASTM-D6751 and EN-14214 standard limits of 3 and 8 h respectively. The results show that the presence of a metal in argemone oil results in accelerating the free radical oxidation reaction. To meet the desired standards, present work experimentally investigates the effect of various antioxidants like BHT, BHA, TBHQ, PY, and PG in the range of 100–500 ppm on argemone oil biodiesel. Effectiveness order of antioxidants in pure biodiesel was observed as: PY > PG > BHA > BHT > TBHQ. The 500 ppm of most effective antioxidant pyrogallol (PY) has the potential to enhance the induction period of argemone biodiesel above 8 h which is vital by EN-14214 standard. Based on the results of most effective antioxidant PY and varying concentration of metals (Fe, Ni, Mn, Cu, and Co), several correlations have been developed to calculate the induction period of argemone oil biodiesel, as a function of antioxidant and metal concentration.

Brain oxidative stress in rat with chronic iron or copper overload

Male rats of 80–90 g that were fed 42 days with a commercial rodent diet of 2780 kcal/100 g and received chronic overloads of either Fe(II) or Cu(II) in the drinking water. The two metals produced brain oxidative stress and damage with marked increases in the indicators of oxidative processes: in vivo brain surface chemiluminescence (the sensitive organ non-invasive assay for oxidative free radical reactions), and the ex vivo processes of phospholipid peroxidation and protein oxidation. Brain redox imbalance was also indicated by marked decreases in the cellular indicators of oxidative metabolic stress: reduced glutathione (GSH) content and reduced/oxidized glutathione ratio (GSH/GSSG). Brain decreased GSH content has a central role in the biochemical oxidative processes associated with Fe and Cu chronic damage. The understanding of biochemical oxidative imbalances in the rat brain with chronic Fe(II) or Cu(II) overloads may be useful for the establishment of pharmacological therapies for human pathologies associated to Fe and Cu cellular imbalances.

Исследование безопасности применения бензилпенициллина натриевой соли после воздействия на нее импульсным магнитным полем

Pulsed magnetic fields are widely used in various fields of modern technology. In our previous works it was shown the strengthening of antibacterial properties of benzylpenicillin sodium salt after exposure to a pulsed magnetic field of high tension. The reason for this may be a change in the conformation of β-lactam antibiotics under external physical influence, which increases the affinity of benzylpenicillin molecules to the active center of penicillin-binding proteins. This article presents studies on the safety of benzylpenicillin sodium salt irradiated by a pulsed magnetic field. Benzylpenicillin sodium salt in powdered form was irradiated with a pulsed magnetic field with the intensity H = (0.09∙106-1.23∙106) A/m, frequency f = 30-70 kHz, and a different number of pulses (n = 1-3), using inductors – single-turn and multi-turn. The influence of pulsed magnetic field on chemiluminescence parameters of irradiated benzylpenicillin sodium salt was studied. The appearance of free radicals in irradiated preparations was evaluated in simple model systems simulating the most common free radical oxidation reactions in the body and in environments in which the formation of reactive oxygen species and lipid peroxidation reactions was initiated. Acute toxicity in intraperitoneal administration of antibiotic to mice before and after treatment with pulsed electromagnetic field with calculation and comparison of LD50 indices was also investigated. It was found that the treatment of the dry substance benzylpenicillin sodium salt by a pulsed magnetic field does not cause the formation of free radicals and is not accompanied by an increase in the toxicity of this antibiotic. The possibility of using new ways to increase the antibacterial activity of antibiotics without increasing their concentrations is considered.

Disadaptive Disorders of Regulation of Functions with Aging

This review examines the basic theories of aging, which show the irreversibility of this process that leads to the death of cells and the body. The hypotheses of phenoptosis and apoptosis are discussed, as well as the view that disadaptation initiates free radical oxidation reactions and violates the neurohumoral regulation of functions. The review briefly examines the mechanisms of the development of age-related diseases. The hypothesis that partial adaptation and disadaptation are transitional biological processes associated with aging is proposed. A regularity that manifests itself in a reduction of the functional activity of an organ and cell metabolism in the state of disadaptation and aging (the principle of the limitation of cellular metabolism) is described. The study shows that aging leads to the progression of homeostatic disorders and changes in DNA methylation processes. The problem of the use of antioxidants, endogenous peptides, telomerase, and ozone to prevent the negative effects of oxidative stress on biomolecules and cellular structures is considered. It was proposed that the biosynthesis of biogenic amines significantly decreases during disadaptation and aging, which entails a decrease in the regulatory control of biochemical reactions by the hypothalamic-pituitary system. It is proposed that biogenic amines and their derivatives be considered substances that minimize the dysregulatory processes that reduce disadaptive manifestations in the body, stimulate cellular metabolism, and slow the aging process.

Redox dyshomeostasis in the experimental chronic hepatic overloads with iron or copper

Male rats of 80–90 g were overloaded with either Fe(II) or Cu(II) for 42 days by high concentrations of FeCl2 or CuSO4 in the drinking water. The animals were fed with a commercial rodent diet of 2780 kcal/100 g. Both metal treatments led to a liver redox imbalance and dyshomeostasis with oxidative stress and damage and the concomitant enhancement of oxidative processes as indicated by in vivo surface liver chemiluminescence, the sensitive and organ non-invasive assay for oxidative free radical reactions, and by ex vivo determined processes of phospholipid peroxidation and protein oxidation. In parallel, marked decreases in the antioxidant defense were observed. Liver reduced glutathione (GSH) content and the reduced/oxidized glutathione ratio (GSH/GSSG) were early indicators of oxidative metabolic disturbance upon the metal overloads. Thus, GSH plays a central role in the defense reactions involved in the chronic toxicity of Fe and Cu. Chronic overloads of Fe or Cu in rats afford an experimental animal model of hemochromatosis and of Wilson's disease, respectively. These two animal models could be useful in the study and development of the beneficial effects of pharmacological interventions in the two human diseases.

The antioxidant activity in patients with chronic obstructive pulmonary disease and ischemic heart disease

New data on the role of the antioxidant system in the mechanisms of the pathogenesis of chronic obstructive pulmonary disease (COPD) and in combination with coronary heart disease (CHD) have been studied. An effective micromethod for the assessment of total antioxidant activity in human blood plasma has been defined. The ambiguous nature of the oxidant/antioxidant system changes in COPD as well as effects of tobacco smoke have been outlined. It has been shown that at the cardiorespiratory pathology aggravation, the free radical oxidation reactions enhance, but with aging, the nonspecific changes are observed. Information on the effectiveness of various antioxidant drugs in the treatment of COPD and in combination with CHD is given. Prospects for the development of research in the individual selection of medications are outlined.

An expedient synthesis of murrayaquinone A via a novel oxidative free radical reaction

Murrayaquinones A–D is a group of four bioactive carbazole-1,4-dione natural products isolated from the root bark of the plant Murraya eucrestifolia hayata. Murrayaquinone is synthesized in five steps starting from the commercially available 2,4,5-trimethoxybenzaldehyde with an overall yield of 45%. The novelty of this murrayaquinone synthesis is in the use of a Mn(OAc)3 mediated oxidative radical reaction of a N-benzylaminoquinone derivative with 2-cyclohexen-1-one for the late-stage indole ring construction.

Determination of total phenolic content and antioxidant activitity of methanol extract of Maranta arundinacea L fresh leaf and tuber

Maranta arundinacea L is one of herbaceous plants in Indonesia which have flavonoid content. Flavonoids has antioxidants activity by inhibition of free radical oxidation reactions. The study aims were to determination total phenolic content and antioxidant activity of methanol extract of fresh leaf and tuber of M. arundinacea L by UV-Vis spectrophotometer. The methanol extracts were obtained with maceration and remaseration method of fresh leaves and tubers. The total phenolic content was assayed with visible spectrophotometric using Folin Ciocalteau reagent. The antioxidant activity was assayed with 1,1-diphenyl-2-picrilhidrazil (DPPH) compared to gallic acid. The results showed that methanol extract of tuber and fresh leaf of M. arundinacea L contained phenolic compound with total phenolic content (TPC) in fresh tuber of 3.881±0.064 (% GAE) and fresh leaf is 6.518±0.163 (% b/b GAE). IC50 value from fresh tuber is 1.780±0.0005 μg/mL and IC50 fresh leaf values of 0.274±0.0004 μg/mL while the standard gallic acid is IC50 of 0.640±0.0002 μg/mL.

ChemInform Abstract: Manganese(III) Acetate Mediated Oxidative Free‐Radical Reactions of 2‐(Alkenylamino)‐1,4‐naphthoquinones with 1,3‐Dicarbonyl Compounds.

The manganese(III)-mediated oxidative free-radical reactions of 2-(alkenylamino)-1,4-naphthoquinones are described. The free-radical reaction of 2-(allylamino)-1,4-naphthoquinone with 1,3-dicarbonyl compounds provides a novel method for the synthesis of benzo[f]indole-4,9-diones and benzo[g]quinoline-5,10-diones. The reaction shows high chemoselectivity, depending on the solvents and 1,3-dicarbonyl compounds used. With both 1,3-diones and β-keto esters, in acetic acid, the condensation products, benzo[f]indoles, were generated selectively; in acetonitrile, the [5+1]-cyclization products, benzo[g]quinolines and tetrahydrobenzo[g]quinolines, were produced in high chemoselectivity. With diethyl malonate, the [5+1]-cyclization product, the corresponding tetrahydrobenzo[g]quinoline, was produced exclusively. The free-radical reaction of a 2-(vinylamino)-1,4-naphthoquinone with 1,3-dicarbonyl compounds produced benzo[g]quinolines effectively.

Antioxidant Effect on the Growth And Formation of Lipids in the Fungus Lentinus tigrinus Growing on Medium with Lignosulfonate

The addition of an antioxidant (2-ethyl-6-methyl-3-hydroxypyridine hydrochloride) to a culture of the fungus Lentinus tigrinus growing on a medium with lignosulfonate inhibited growth and changed the composition of cell phospholipids. The ratio of lipid messengers also changed, the phosphatidic acid level decreased, and the content of phosphatidylinositol dramatically increased. The substitution of lignosulfonate with glucose and the addition of an antioxidant increased the biomass yield of L. tigrinus, as well as that of another fungus, Cunninghamella japonica, which was incapable of biodegrading the biopolymer. The obtained results indicate the specificity of growth processes in the presence of lignosulfonate and confirm the role of free radical oxidation reactions in the biodegradation of this biopolymer by L. tigrinus.